Method for a hydraulic system for a dual-clutch gearbox

Abstract

A hydraulic system for an automatic gearbox for a motor vehicle, includes a high-pressure circuit which includes a pressure accumulator, at least one clutch and actuators, and a low-pressure circuit for cooling the clutch, the high-pressure circuit and the low-pressure circuit each containing a hydraulic cooling pump and a hydraulic charging pump that can be driven by a shared electric motor; and a controller which, when it is detected that the pressure accumulator needs to be charged, controls the electric motor to run at a charging setpoint speed, and/or, when it is detected that cooling is needed or another need exists, controls the electric motor to run at a cooling setpoint speed or another setpoint speed. The electric motor is paired with a current measuring device for measuring an actual current consumption and a rotational speed sensor for measuring an actual rotational speed. The controller has an analysis unit which uses the actual current consumption and the actual rotational speed, specifically from the comparison of the actual current consumption with a reference value, to detect a need for charging of the pressure accumulator.

What is claimed is: 
     
       1. A hydraulic system for an automatic transmission, comprising:
 a high-pressure circuit comprising a pressure accumulator, at least one clutch, and actuators; 
 a low-pressure circuit for cooling the at least one clutch, said low-pressure circuit comprising a cooling hydraulic pump and a charging hydraulic pump which are drivable via a shared electric motor; 
 a current measuring device for detecting an actual current consumption of the electric motor; 
 a speed sensor for detecting an actual speed of the electric motor; 
 a control device having an analysis unit and a constant-speed unit, 
 said analysis unit recognizing a requirement for charging the pressure accumulator as a function of the actual current consumption and the actual speed of the electric motor measured by the current measuring device and the speed sensor, 
 said control device controlling the electric motor to run at a charging setpoint speed when the analysis unit recognizes a requirement for charging the pressure accumulator or controlling the electric motor to run at a cooling setpoint speed or other setpoint speed when the analysis unit recognizes a requirement for cooling or other requirement, 
 said constant-speed unit detecting whether the hydraulic pumps run at a constant speed, wherein when the hydraulic pumps do not run at a constant speed the analysis unit is deactivated and when the hydraulic pumps run at a constant speed the analysis unit is activated. 
 
     
     
       2. The hydraulic system of  claim 1 , wherein the analysis unit determines the requirement for charging the pressure accumulator based on a comparison between the actual current consumption and a reference value which is determined based on a reference value polynomial stored in the control device in dependence on the actual speed. 
     
     
       3. The hydraulic system of  claim 2 , wherein the reference value polynomial is generated in an initialization phase, and wherein in the initialization phase, at different actual speeds the corresponding actual current consumptions are detected as reference values and stored. 
     
     
       4. The hydraulic system of  claim 2 , wherein the analysis unit recognizes the requirement for charging the pressure accumulator based on a comparison between the actual current consumption and a filtered value of the actual current consumption. 
     
     
       5. The hydraulic system of  claim 2 , wherein after generation of the reference value polynomial the requirement for charging the pressure accumulator is recognizable from a comparison of the actual current consumption with the reference value. 
     
     
       6. The hydraulic system of  claim 1 , wherein the constant-speed unit determines that the hydraulic pumps run at a constant speed when a setpoint speed gradient is zero, a filtered setpoint speed gradient is smaller than a threshold value, and an actual rotational speed gradient is smaller than a threshold value. 
     
     
       7. The hydraulic system of  claim 1 , wherein in a non-charging mode of the hydraulic system, the cooling hydraulic pump and the charging hydraulic pump are fluidly connected with the low-pressure circuit and the charging hydraulic pump is decoupled from the high-pressure circuit, and wherein in the non-charging mode the hydraulic pumps operate at reduced pump load and reduced actual current consumption. 
     
     
       8. The hydraulic system of  claim 7 , wherein in a charging mode of the hydraulic system, the charging hydraulic pump is fluidly connected with the high-pressure circuit and operates at increased pump load with increased actual current consumption. 
     
     
       9. The hydraulic system of  claim 1 , wherein the high-pressure circuit and the low-pressure circuit are connected via a bypass line with an integrated control valve, said control valve being configured to automatically switch in dependence on an accumulator pressure in the high-pressure circuit without external energy input between a charging position in which the hydraulic system operates in a charging mode and a non-charging position in which the hydraulic system operates in a non-charging mode. 
     
     
       10. The hydraulic system of  claim 9 , wherein the control valve automatically assumes the charging position when an accumulator pressure in the high-pressure circuit falls below a lower threshold value and the control valve automatically assumes the non-charging position when the accumulator pressure in the high-pressure circuit exceeds an upper threshold value. 
     
     
       11. The hydraulic system of  claim 10 , wherein the control device has a pressure model unit which detects during operating time actuations of the actuators or other events that influence a pressure of the accumulator and in dependence on the actuators and other events generates partial pressure differences, wherein at a charging mode end time point, the accumulator pressure in the high-pressure circuit corresponds to the upper threshold value, wherein when exceeding the upper threshold value, the control valve in the bypass line automatically switches from the charging position into a cooling position, wherein the upper threshold value is an initial pressure of the pressure model unit from which the partial pressure differences are subtracted or added. 
     
     
       12. The hydraulic system of  claim 11 , wherein the partial pressure differences are due to actuation of the actuators and/or loss of hydraulic fluid. 
     
     
       13. The hydraulic system of  claim 10 , wherein the control device has a pressure model unit which detects during operating time actuations of the actuators or other events that influence a pressure of the accumulator and in dependence on the actuators and other events generates partial pressure differences, wherein the accumulator pressure in the high-pressure circuit is continuously reduced with a substantially constant slope due to pressure loss as a result of loss of hydraulic fluid, and wherein the accumulator pressure is substantially abruptly reduced due to an actuator actuation. 
     
     
       14. The hydraulic system of  claim 13 , wherein the pressure model unit for simulating the decrease of the accumulator pressure over time estimates or determines the slope. 
     
     
       15. The hydraulic system of  claim 14 , wherein the pressure model unit calculates the slope based on a time interval between the charging mode end time point and a subsequent charging mode starting time point and based on a pressure difference between the upper threshold value and the lower threshold value of the control valve by taking the partial pressure differences that have occurred in the time interval into account. 
     
     
       16. The hydraulic system of  claim 1 , wherein in absence of a requirement for cooling or other requirement and also in the absence of a requirement for charging the pressure accumulator, the control device controls the electric motor to run at a test rotational speed for detecting the actual speed and the actual current consumption, said test rotational speed being lower than the charging setpoint speed and the cooling setpoint speed. 
     
     
       17. The hydraulic system of  claim 16 , wherein in absence of the requirement to charge the pressure accumulator and in absence of the requirement for cooling or other requirement, the control device lowers the setpoint speed to zero for a predetermined time period, and wherein after expiration of the predetermined time period, the control device controls the electric motor to run at least at the test rotational speed. 
     
     
       18. The hydraulic system of  claim 17 , wherein the control device has a pressure model unit which detects during operating time actuations of the actuators or other events that influence a pressure of the accumulator and in dependence on the actuators and other events generates partial pressure differences, said pressure model unit simulating a decrease of the pressure of the accumulator over time during the predetermined time period as a function of the detected partial pressure differences. 
     
     
       19. The hydraulic system of  claim 18 , wherein when reaching a minimal pressure in the pressure model unit, the control device controls the electric motor to run at least at a test rotational speed. 
     
     
       20. The hydraulic system of  claim 18 , wherein the pressure model unit simulates the decrease of the pressure of the accumulator over time additionally on the basis of a pressure loss due to a loss of hydraulic fluid. 
     
     
       21. A motor vehicle, comprising the hydraulic system of  claim 1 . 
     
     
       22. A method for operating a hydraulic system, comprising:
 determining with a current-measuring device an actual current consumption of an electric motor of a high-pressure circuit of the hydraulic system, said high-pressure circuit further comprising a pressure accumulator, at least one clutch, and actuators, said electric motor driving a respective cooling hydraulic pump and charging hydraulic pump of a low pressure circuit, said low-pressure circuit being configured for cooling the at least one clutch of the high pressure circuit; 
 determining with a speed sensor an actual speed of the electric motor; 
 recognizing with an analysis unit of a control device a requirement for charging the pressure accumulator as a function of the actual current consumption and the actual speed of the electric motor measured by the current measuring device and the speed sensor; 
 controlling the electric motor with the control device to run at a charging setpoint speed when the analysis unit recognizes a requirement for charging the pressure accumulator; or 
 controlling the electric motor to run at a cooling setpoint speed or other setpoint speed when the analysis unit recognizes a requirement for cooling or other requirement; 
 detecting with a constant-speed unit of the control device whether the hydraulic pumps run at a constant speed; and 
 deactivating the analysis unit when the hydraulic pumps do not run at a constant speed and activating the analysis unit when the hydraulic pumps run at a constant speed.